# Questions tagged [functions]

Questions about the use of built-in Mathematica functions, including pure functions.

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### Simplifying an ODE in Bessel notation

I have the following Mathematica code: eq[r_] = 3 (1 + 2 a) g1 r y[r] - 2 (2 y'[r] + r y''[r]); DSolveValue[eq[r] == 0, y[r], r] This gives me the ...
• 2,445
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### Limit of a PolyLog does not work [bug]

I tried the following code, but it does not work as expected: ...
32 views

### Defining new functions from old function throws error [closed]

I am trying to define a new function from an old function but it is not working properly. ...
• 121
1 vote
130 views

### Help with the visualization of a function

I am trying to make the plot of an specific function through integration from others, but Wolfram-Alpha and Desmos are having problems with it, so I came here to see if someone could help me using ...
• 175
1 vote
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### Automate adding nullclines to StreamPlot

I have the system $$x' = x^2$$ $$y'= y(2x - y)$$ We can calculate the nullclines by solving the first equation for $y$, but since there is no $y$ it is just $x=0$. For the second equation, we get the ...
• 3,400
28 views

### How to edit the DumpSave data file later?

My understanding is, if you store something through DumpSave in a file, and then, on a later session, try to use the same file to save some more data, the older data will get erased. Is this true? Is ...
• 121
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### Setting shared function values in parallel is running sequentially

I am trying to define a function whose values can be updated across different Kernels running in parallel, where each Kernel might have to use values defined by other Kernels previously in the process....
• 1,136
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### Square3D Graphics Object

I wonder why there is no generalization of objects like Rectangle to Graphics3D included in the software. Does anybody know the ...
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292 views

### How to make an operator form of Part[] to use with // (Postfix)

I've often found myself chaining multiple functions in Mathematica using the // postfix form, and then needing to extract specific parts of the result. The standard ...
33 views

### Findminimum to optimize a module function, [closed]

I have a complex module with single output: In[3526]:= opti[1, 0, 0] Out[3526]= 0.1942056308 When I use findminimum to get minimal output ...
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1 vote
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### Why is the result of this integration coming out as a list if the function being integrated just returns a numerical value?

I am trying to integrate over a Dirichlet distribution. Instead of using the built-in function, I defined it myself as: ...
269 views

### What is a simpler method to find the analytical expression for the function f[x]?

Given the following conditions, find the analytical expression for the function f[x] f[Sqrt[x] + 1/Sqrt[x]] == x + 1/x My method is as follows: ...
• 4,697
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### "SixJsymbol" function unable to be simplified with long run times due to not real components despite including the assumptions

I'm trying to perform some quantum mechanical calculations using Wigner-Eckhart theorem by running them through Mathematica. However, despite including the assumptions the calculation is unable to be ...
1 vote
90 views

### Evaluating step functions [closed]

Please guys, how do I tell Mathematica to return f(a-b)= 1 if a=b and 0 otherwise? This means that f(0)=1 and f(x)=0 for x>0.
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### Function argument with tree type

I liked to define a function argument type representing a tree with only nodes: 0,1. Every subtree is defined as a list like this: {node,{subtree1},{subtree2},...} The definition is recursive. The ...
52 views

### How does InternalStringToMReal work and is this a bug

I was under the impression that InternalStringToMReal removed string characters that were not digits and converted those to numbers. However this fails on "OE2", see below. Is my ...
45 views

### What other methods are there to solve the problem of determining whether this function inequality is correct or not?

Question: Given that the domain of function $f(x)$ is $R$, $f(x)>f(x-1)+f(x-2)$, and when $x<3$, $f(x)=x$, which of the following conclusions must be correct? A. $f(10)>100$ B. $f(20)>1000$...
• 4,697
61 views

### Issue solving a recurrence relation

I´m trying to solve the following recurrence relation in Mathematica: ...
• 145
232 views

### Why does FindInstance[x>0,x] give 27? [closed]

Why does FindInstance[x>0,x] give 27? I would think it would give 1… maybe 2 or some small positive decimal.
• 1,627
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### Issue solving recurrence relation

I´m trying to solve the following recurrence relation: ...
• 145
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### Why doesn't Conjugate[] conjugate exponentials inside other functions?

Why does something like Conjugate[Sqrt[Exp[I x]]] give output Conjugate[Sqrt[E^(I x)]] instead of ...
229 views

### How to optimize performance with DeleteDuplicates?

Does anyone know how to improve this for speed performance? The code works fine, but DeleteDuplicates makes it really slow for large lists. ...
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1 vote
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